The present invention relates to a device for moving a jet member having a nozzle, said device comprising                a carriage provided with a base portion to which said jet member is connected,        a guide member along which said carriage is movable in a substantially rectilinear first path for moving the nozzle of the jet member over a layer to be treated by the jet,        the connection of said jet member to said base portion providing a movability of the jet member with respect to the base portion and by that said carriage comprising a first movability of the jet member for moving an impact point of said jet in a second path perpendicularly to said first path,        a driving arrangement configured to move said carriage along said first path and said jet member with respect to said base portion of said carriage, and        a control unit configured to control said driving arrangement for controlling the movement of said impact point of said jet over a said layer,as well as a method.        
This treatment of a material layer is first of all intended to be a material removing treatment. Although the layer may consist of other material a concrete layer is preferably concerned herein. Primarily, the treatment is intended to have the purpose to remove weakened material from the layer. It may then be a question of removing weakened concrete from concrete layers on roads, bridges and a variety of building structures, whereupon the removed concrete may be replaced by new concrete. It is in this connection especially preferred that the treating member is constituted by a jet member so as to direct a high pressure jet of liquid against the material layer. Thus, it is this high pressure jet of liquid which executes the material removing treatment. Preferably, the high pressure liquid consists of water. Although the definition “impact point” is used in this disclosure for the place where the jet hits said layer it is really not a question of a point, but a smaller restricted area on which the jet hits said layer. Said movability of the jet member with respect to the base portion of said carriage normally also includes a pivotability of the jet member around an axis perpendicular to said first path for changing the attack angle, but the present invention is not restricted to the case that a possibility to change the attack angle exists. A desire to change the attack angle is due to the fact that said concrete layers are reinforced by reinforcement bars, normally in a lattice-like structure. By using a small attack angle, i.e. an angle of the jet being substantially perpendicular to the layer to be treated, the material may be removed quickly, but the result of the treatment will not be that uniform. However, by choosing a large attack angle of the jet the jet will easier reach under the reinforcement bars, so that it will be cleaner thereunder and the result of the treatment will be more uniform and the surface treated smooth.
Said first movability is normally accomplished by a pivoting of the jet member around an axis extending in parallel with said first path in the form of oscillations when moving the carriage and by that the jet member along said guide member in said first path and is carried out for obtaining a broader stripe of the layer surface treated by the jet when moving this along said first path. The width of such a stripe treated by the jet member may be in the order of 20-100 mm when the carriage moves along the guide member, which means that the device may then be indexed at a maximum by this width for treating a further stripe of the layer.
This type of oscillations around a said axis in a device of this type is shown in for example EP 1 029 127 B1. It is schematically shown in appended FIG. 1 how the impact point of the jet member moves over the material layer treated when combining a movement along said first path in the direction X with an oscillation around an axis in the direction Y. The speed of travel of said impact point over said layer by these combined movements will differ, since the pivoting will have a neglectable contribution to that speed near the end positions e of said second path and have a significant contribution to that speed in regions therebetween. This means that the exposure time of the layer for said jet member (impact point) will be longer at said end positions resulting in a deeper material removal there resulting in a formation of so called pits or bore holes. These may get a depth of 15-40 mm and a diameter of 10-20 mm, although other figures are possible depending upon the structure of the material treated. It will then be difficult to fill these pits with concrete when subsequently applying new concrete on the layer treated, and unacceptable air pockets or enclosures may then be formed in the bonding area of new concrete to old concrete. Such pockets may be filled by moisture which may result in loosening of the new concrete upon temperature changes. This has to be avoided, which is especially difficult in the case of a material layer in the form of a vertical wall or ceiling treated. It will then be impossible to utilize the gravity to shake the concrete to penetrate into and fill said pits.